The arbuscular mycorrhizal fungus Rhizophagus irregularis affects arthropod colonization on sweet pepper in both the field and greenhouse

In the present study sweet pepper plants, Capsicum annuum, were planted in greenhouse and open field conditions to test the effect of the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis on phytophagous and predatory arthropod populations. Furthermore, we tested the hypothesis that AMF may increase the crop yield (number of fruits and their weight) and activity level of polyphenol oxidase (PPO) and peroxidase (POD), enzymes that seemingly decrease infestation by arthropod pests. The most abundant arthropod species found were the peach-potato aphid, Myzus persicae, western flower thrips, Frankliniella occidentalis, and the seven-spot ladybird, Coccinella septempunctata. Sweet pepper mutualism with AMF significantly reduced colonization by the peach-potato aphid under greenhouse conditions. Aphid density increased, however, on two of four pepper varieties tested under open field conditions. The density of ladybird predators did not appear directly influenced by AMF under greenhouse conditions, whereas a significantly higher predator density was found on three out of four pepper plant varieties with fungal mutualism tested under field conditions. Crop yield was significantly higher on plants with AMF mutualism under greenhouse conditions, but no clear effects were detected under field conditions. Both PPO and POD activity increased significantly and remained higher than controls until day 14 of the experiment under mutualism with AMF, although only in the greenhouse. The results suggest that under greenhouse conditions, pepper plant mutualism with AMF can increase pepper yield by reducing the numbers of the key pest, peach-potato aphid.